1. Technical Field
The present invention relates, generally, to rechargeable battery systems including a main and a reserve battery disposed for intermittant electrical communication, and more particularly to vehicle battery systems wherein both batteries are configured within a housing having conventional external dimensions.
2. Background Art and Technical Problems
Vehicle battery systems having a main and a reserve unit, separated by a one-way diode for maintaining the reserve unit in the charged condition during non-use, are generally known. The diode allows current to flow from the vehicle generator into the reserve battery, but prevents the reserve battery from discharging through the current path including the diode. Diodes are problematic, however, in that they exhibit a limited current carrying capacity. Diodes having a relatively low current carrying capacity may be blown if excessive current is driven therethrough, whereas diodes having higher current ratings typically dissipate correspondingly large amounts of thermal energy. For example, commercially available diodes typically exhibit a voltage drop of approximately 0.7 volts thereacross. Thus, a diode having 25 amps running therethrough radiates approximately 17.5 watts. Consequently, various design parameters associated with the diode environment, for example, proximity to plastics and volatile chemicals, availability of heat sinks, diode size, and production costs are circumscribed by the heat-generating character of diodes.
In the context of the dual battery of the present invention, the terms "reserve unit" and "reserve battery" refer to a low cycle auxiliary battery configured for intermittent use, as distinguished from "reserve capacity," a term of art referring to the length of time a battery is capable of delivering, for example, twenty-five (25) amperes under given conditions. Furthermore, it will be understood that the word "termination" as used herein describes an electrical contact associated with a battery element, typically an element located at an end of a battery (the terminal element). Each terminal element may have one or more terminations associated therewith for carrying current to or from the battery. Each individual battery generally has a positive termination associated with one end thereof and a negative termination associated with the opposite end. Terminations which extend through the battery housing for attachment to a load are referred to as terminals, and may be cylindrical, frustroconical, flanged, L-shaped, or D-shaped, for example. Terminations which do not extend through the housing or which do not communicate directly with a load are typically configured for electrical communication with an adjacent battery, and are referred to as "flush terminations".
Prior art dual battery systems have proven unreliable and cumbersome. A switchable dual battery, for example, one disclosed by Pacific Dunlop of Australia, comprises a series of thin, flat, parallel electrode plates. A first portion of the plates comprises the main battery and a second, adjacent portion parallel to the first portion comprises the reserve battery. The two batteries are linked by a switch mechanism for controlling the discharge of the reserve unit. Each battery purportedly delivers 12 volts, the main battery being rated at 370 CCA (cold crank amps) and the reserve battery at 115 CCA. The two batteries are electrically configured in parallel, with a one-way diode disposed therebetween to prevent the reserve unit from discharging during periods of non-use. A manually operable switch is interposed between the two batteries, in parallel with the diode, to bypass the diode when it is desirable to discharge the reserve unit. If the switch is inadvertently left in bypass (shunt) mode, however, the reserve unit will discharge along with the main unit, thereby impairing the ability of the reserve unit to function as an auxiliary starting battery. When the switch is open, on the other hand, the diode may be blown if excessive current is drawn therethrough during charging of the reserve battery.
A Power Reserve Battery system, bearing the name DELCO POSIPOWER, has been observed in certain 1985 model automobiles. The battery housing has three external terminals extending from the cover: a main battery positive terminal; a reserve (starter) battery positive terminal; and a common negative (ground) terminal.
The negative terminal electrodes of each battery in the DELCO POSIPOWER system are purportedly connected through a link in the battery housing cover assembly. Thus, a vehicle electrical system requires three cables to accomodate the POSIPOWER system. The cable from the positive terminal of the reserve battery is connected to a solenoid which is activated during starting; the solenoid and starting circuit are located in a control box remote from the battery housing. Each time the ignition key is turned to the "start" position, the main battery latches the solenoid to bring the reserve battery into parallel with the main battery. When the cranking cycle is complete, the solenoid unlatches, again isolating the reserve battery. In the event the main battery lacks sufficient power to energize the latching solenoid, a bypass system, located in the control box, may be manually activated to establish communication between the reserve battery and the starting circuit.
The performance of these prior art battery systems has been unsatisfactory. In particular, retrofitting vehicles to accommodate different sized battery housings, different terminal configurations, or remote circuitry is often cost prohibitive. System reliability may be impaired if diodes with insufficient current-carrying capacity are employed (the diode may be destroyed), whereas safety and performance are compromised when high current capacity diodes are used because of the excessive heat generated thereby. Moreover, presently known dual battery configurations do not permit disposition of two batteries, each capable of delivering sufficient power to start a vehicle, within a housing defined by a conventional vehicle battery envelope and having terminal locations designed to accommodate conventional vehicle cable configurations.